Such prior application discloses and claims certain improvements in electrical surveys of underground or underwater structures such as pipelines. As indicated in such prior application, surveys utilizing an established pipe-to-electrolyte potential may be continued utilizing fixed-to-moving-cell potentials if the proper corrections are made.
It has been discovered that for certain applications, such fixed-to-moving-cell surveys may be utilized either before or after (upstream or downstream) obtaining an established pipe-to-electrolyte potential, either by one or more direct electrical connections to obtain a point or points of established potential, or by a survey with a direct electrical connection. In other words, the cell-to-cell survey may be conducted either before or after a direct wire connection survey, or either before or after a single point electrical connection to obtain an established potential, with the cell-to-cell survey results being corrected by a summation of the cell-to-cell results and the established potential at the same location to obtain a reliable electrical survey of the structure.
In many situations where surveys are desired for relatively short lengths of submerged structures such as pipeline it is not possible to establish a structure-to-electrolyte potential at the desired location. Nor is it necessarily possible to maintain that established potential throughout the course of the desired survey. Thus it has been found that corrected cell-to-cell surveys conducted either before or after (following) the established structure-to-electrolyte potential may be quite useful if the results are properly correlated and corrected.